The present invention relates to a process chamber for processing semiconductor substrates.
Control of the temperature of process chambers that are used to etch, implant, or deposit material on semiconductor substrates, is necessary to provide reliable and reproducible semiconductor fabrication processes. Many of these processes are highly temperature dependent and provide different processing rates or characteristics at different temperatures. Temperature fluctuations of a chamber are particularly undesirable during sequential processing of a batch of substrates, because the substrates are processed with different properties. For example, in etching processes, temperature fluctuations can cause the shape of the etched features on the substrate to vary widely from one substrate to another, and to vary as a function of the temperature profile across the substrate. Also, large temperature fluctuations of the chamber components or walls can cause residues that deposit on the chamber walls or ceiling to flake off and contaminate the substrate.
Another temperature control problem arises when the chamber walls and surfaces are made of ceramic materials, such as silicon, B4C or BN. Some ceramic materials have a low thermal shock resistance and crack when subjected to thermal stresses resulting from large variations in temperature across the ceramic component. For example, a chamber wall is made from a ceramic material, such as aluminum oxide which has a low tolerance to thermal stress, when inductor coils are used to couple RF energy into the chamber. Also, other ceramic materials that have high thermal expansion coefficients undergo a large expansion or contraction for even a small temperature change causing the wall to break or crack when subjected to widely different temperatures. It is desirable to control the temperature of the ceramic surfaces of process chambers and to reduce their temperature fluctuations.
Conventional temperature control systems for semiconductor process chambers include xe2x80x9cwater-jacketxe2x80x9d liquid-recirculating systems or forced-air cooling systems. However, in many process chambers, complex shaped components, such as inductor coils, which are positioned next to the chamber surfaces make it difficult to transfer heat to and from the chamber surfaces in the gaps or narrow spaces between these components. In addition, liquid recirculating systems typically circulate water through a large number of channels that have small diameters, providing a bulky system that is difficult to attach or couple to the chamber without forming contact areas of high thermal resistance. Also, the channels and circulating liquid absorb RF induction energy and cannot be used near inductor components that transmit RF energy into the chamber. In addition, inadequate arrangement of the channels of the recirculating system often result in instabilities and localized hot spots around the components on the chamber.
Forced-air cooling systems, as for example, described in U.S. Pat. No. 5,160,545, issued Nov. 3, 1992, use fans to blow cooled air past chamber surfaces. These systems often cause localized hot spots at portions of the chamber that are shielded from the air flow. Also, because the primary mode of heat transfer is conduction by air, forced air cooling systems typically require an extremely large air flow to achieve even a moderately acceptable response time to large temperature fluctuations in the chamber, such as the temperature fluctuations caused by turning on and off the plasma or other heat loads in the chamber. The large air flow rates also typically require large fans, which are more prone to mechanical failure, and upon failure, can severely damage chamber components.
Thus it is desirable to have a process chamber having a temperature control system capable of providing uniform temperatures and reducing large temperature fluctuations in process chambers. It is further desirable for the temperature control system to control temperatures during widely varying thermal loads. It is also desirable to have a temperature control system that does not interfere with the operation of electrical chamber components, and in particular, does not dissipate or attenuate inductively coupled RF energy. It is further desirable for the temperature control system to reduce or eliminate thermal stresses on the chamber surfaces, particularly the ceramic surfaces.
The present invention relates to a process chamber providing improved temperature control during processing of a semiconductor substrate in the chamber. The process chamber comprises a support, a process gas distributor, a heat transfer member having a heat conduction surface bonded to an external surface of the process chamber, and an exhaust. The substrate is held on the support in the process chamber. Process gas is introduced into the process chamber, and optionally, RF energy is coupled to the process gas to sustain a plasma of the process gas. The process gas or plasma is used to process the substrate, and thereafter is exhausted by the exhaust. A flow of heat to and from the process chamber is regulated via the heat transfer member that is bonded to the external surface of the process chamber. Preferably, the heat transfer member comprises a heat conduction surface having an RMS peak-to-peak roughness of less than about 500 microns.
In a preferred version, the process chamber further comprises a ceiling comprising semiconductor material having an electrical susceptibility that is sufficiently low to allow an RF induction field to permeate therethrough, and an inductor antenna adjacent to the ceiling to couple an RF induction field through the ceiling into the process chamber. A temperature control system that is capable of maintaining substantially uniform temperatures across the ceiling, comprises a heat exchanger and a heat transfer member having a heat conduction surface bonded to the ceiling and a heat transmitting surface thermally coupled to the heat exchanger.
In another aspect, the present invention further comprises a method of processing a substrate in a process chamber. The method comprises the steps of placing a substrate in the process chamber, introducing process gas into the process chamber, charging an inductor antenna adjacent to a ceiling of the process chamber to couple RF energy to the process gas to sustain a plasma in the process chamber, and monitoring the temperature of the ceiling and regulating the flow of heat to and from the process chamber via a heat transfer member bonded to the ceiling, a heater, and a heat exchanger.
In yet another aspect, the present invention further comprises a method of bonding a heat transfer member to an external surface of a process chamber. The method comprises the steps of forming a heat transfer member having a heat conduction surface, providing a thermally conducting adhesive between the heat transfer member and the external surface, pressing the heat transfer member against the external surface, and heating the thermally conducting adhesive to cure the adhesive and form a thermally conducting bond between the heat transfer member and the external surface of the process chamber.